1. Field of the Invention
The present invention relates generally to modems (modulators/demodulators), and more particularly to the generation of I (in-phase) and Q (quadrature-phase) carrier signal components in modems.
2. Related Art
There are certain fundamental, high frequency building blocks that are in most wireless communication systems, such as cellular telephone systems. For example, most wireless communication systems employ modems (modulators/demodulators) that require the generation of both I (in-phase) and Q (quadrature-phase) carrier signal components to both transmit and receive data. These modems include a carrier generation circuit to generate such I and Q carrier signal components. Typically, a carrier generation circuit is implemented using a voltage controlled oscillator (VCO) connected to a quadrature (90 degree) phase splitter.
Conventionally, a carrier generation circuit operates at a single frequency. Such single frequency operation is due to the conventional implementation of the VCO and the quadrature phase splitter contained within the carrier generation circuit. Specifically, in VCOs and quadrature phase splitters, critical circuit elements are typically implemented using passive components, such as resistors, capacitors, fixed length transmission lines, etc. As a result, the operational frequency range (i.e., the bandwidth) of such VCOs and quadrature phase splitters is limited to a single frequency. This frequency can only be changed by re-designing and re-implementing the VCOs and quadrature phase splitters.
Since conventional VCOs and quadrature phase splitters are limited to a single operational frequency, it is very difficult to design and implement modems having a wide frequency bandwidth. As a result, conventional modems operate to limit the functionality of the wireless communication systems in which they are used.
Thus, what is required is a carrier generation circuit having a wide frequency bandwidth.